Func<Action> would be a function that takes no arguments and returns an Action. The desire is to be able to specify void as the return type of a Func, so that

Func<Action> would be a function that takes no arguments and returns an Action. The desire is to be able to specify void as the return type of a Func, so that you can use Funcs for all callbacks, instead of having to use Funcs for callbacks that return a value and Actions for callbacks that don't.